Lithium ion capacitor

Abstract

The present invention has as its object the provision of a lithium ion capacitor having high capacity and high output characteristics and also having high safety that allows suppression of an increase in surface temperature even when an internal short circuit accidentally occurs. The lithium ion capacitor of the present invention comprises: a lithium ion capacitor element formed by overlaying a positive electrode sheet and a negative electrode sheet on top of one another with a separator interposed therebetween; an electrolyte solution; and an outer container that contains the lithium ion capacitor element and the electrolyte solution, a porous layer is formed on an outer surface of the lithium ion capacitor element, and the lithium ion capacitor satisfies following relational expressions (1) and (2): 35≦ T×R/C   relational expression (1): 0.01≦ R/C ≦5  relational expression (2): where C is a capacitance [kF] of the lithium ion capacitor, R is a direct current resistance value [mΩ] of the lithium ion capacitor, and T is a thickness [μm] of the porous layer.

The invention claimed is: 
     
       1. A lithium ion capacitor, comprising:
 a lithium ion capacitor element formed by overlaying a positive electrode sheet and a negative electrode sheet on top of one another with a separator interposed therebetween; 
 an electrolyte solution; 
 a lithium ion supply source; and 
 an outer container that comprises the lithium ion capacitor element and the electrolyte solution, 
 wherein a porous layer is formed on an outer surface of the lithium ion capacitor element has a thickness of less than 1,000 μm, 
 wherein the lithium ion capacitor satisfies expressions (1) and (2):
   35≦ T×R/C   (1),
 
   0.01≦ R/C≦ 5  (2),
 
 
 wherein C is a capacitance [kF] of the lithium ion capacitor, R is a direct current resistance value [mΩ] of the lithium ion capacitor, and T is a thickness [μm] of the porous layer, and 
 wherein the lithium ion supply source is disposed in the lithium ion capacitor element such that the lithium ion supply source does not contact the positive electrode sheet and the negative electrode sheet. 
 
     
     
       2. The lithium ion capacitor of  claim 1 , wherein the porous layer is formed by overlaying porous sheets. 
     
     
       3. The lithium ion capacitor of  claim 1 , wherein the porous layer and the separator are formed from a single member. 
     
     
       4. The lithium ion capacitor of  claim 1 , wherein the porous layer comprises at least one selected from the group consisting of cellulose, rayon, polyethylene, and polypropylene. 
     
     
       5. The lithium ion capacitor of  claim 1 , wherein the porous layer has a thickness of not smaller than 120 μm. 
     
     
       6. The lithium ion capacitor of  claim 2 , wherein the porous layer and the separator are formed from a single member. 
     
     
       7. The lithium ion capacitor of  claim 2 , wherein the porous layer comprises at least one selected from the group consisting of cellulose, rayon, polyethylene, and polypropylene. 
     
     
       8. The lithium ion capacitor of  claim 2 , wherein the porous layer has a thickness of not smaller than 120 μm.